1. Field of the Invention
The present invention relates to a thiophene-containing compound and a thiophene-containing compound polymer which are useful for organo-electronic devices such as electrophotographic photoreceptors (photosensitive elements), organic electroluminescent elements and organic transistors. More specifically, the invention relates to a thiophene-containing compound and a thiophene-containing compound polymer which are excellent in both charge-transporting properties and luminous properties.
2. Description of the Related Art
Well-known as charge-transporting materials are charge-transporting polymers represented by a polyvinylcarbazole (PVK) and low-molecular dispersion systems obtained by dispersing a charge-transporting low-molecular compound in a polymer. Among these materials, low-molecular dispersion systems are primarily used for electrophotographic photoreceptors because a variety of materials can be used in such systems, and highly functional products can be readily obtained.
Concomitant with the development in recent years of high performance organic photoreceptors, electrophotographic photoreceptors have been used in high speed copying machines and printers. However, at present the performances of these photoreceptors are still not necessarily satisfactory and further developments thereof are highly desirable, specifically in terms of longer-life. By using as a charge-transporting layer comprising the current main stream low-molecular dispersion system, electrophotographic photoreceptors have been obtained which produce satisfactory performances in respect of electrical characteristics. However, such charge-transporting layers have also revealed deficiencies insofar that they use a low-molecular compound dispersed in a polymer and are intrinsically inferior in mechanical strength, thus resulting in poor abrasion resistance.
Organic electroluminescent elements are generally produced by vapor deposition of low-molecular charge-transporting materials. Organic electroluminescent elements have a drawback insofar that a large quantity of Joulean heat caused by a current density as high as several mA/cm2 tends to cause morphologic changes due to, for example, crystallization of such low-molecular charge-transporting materials. Consequently phenomena such as reduction in luminance and dielectric breakdowns have tended to occur, thus curtailing the lifespans of such organic electroluminescent elementals. Only a limited number of materials have both charge-transporting and luminous properties, and organic electroluminescent elements produced therefrom have therefore tended to be unsatisfactory from the standpoints of both efficiency and longevity.
In contrast, for use as a photoconductive material in the production of electrophotographic photoreceptors, the charge-transporting polymer represented by PVK has considerably overcome the above drawbacks, and hence is being intensively studied (see, for example, The 37th Society of Applied Physics & Related Societies of Japan, Preprints, 31p-K-12 (1990)).
Specifically, a polycarbonate obtained by polymerizing a specific dihydroxyarylamine with bischloroformate (see, for example, U.S. Pat. No. 4,806,443) and a polycarbonate obtained by polymerizing a specific dihydroxyarylamine with phosgene (see, for example, U.S. Pat. No. 4,806,444) have been proposed.
Additionally, a polycarbonate obtained by polymerizing a bishydroxyalkylarylamine with bischloroformate or phosgene (see, for example, U.S. Pat. No. 4,801,517), a polycarbonate obtained by polymerizing a specific dihydroxyarylamine, bishydroxyalkylarylamine or bishydroxyalkylamine with bischloroformate, or a polyester obtained by polymerizing one of the above three amines with a bisacyl halide have been disclosed (see, for example, U.S. Pat. Nos. 4,937,165 and 4,959,228).
Moreover, a polycarbonate prepared from an arylamine having a specific fluorene skeleton, a polyester (see, for example, U.S. Pat. No. 5,034,296), and a polyurethane (see, for example, U.S. Pat. No. 4,983,482) have been proposed.
Further, a polyester containing a specific bisstyrylbisarylamine as a main chain (see, for example, Japanese Patent Application Publication (JP-B) No. 59-28903), a polymer having, as a pendant, a charge-transporting substituent such as hydrazone or triarylamine, and photoreceptors produced therefrom (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 61-20953, 1-134456, 1-134457, 1-134462, 4-133065 and 4-133066) have been proposed.
On the other hand, an organic electroluminescent element produced from a π conjugate polymer represented by paraphenylenevinylene (PPV) (see, for example, Nature, Vol. 357, 477 (1992)) and an organic electroluminescent element produced from a polymer in which triphenylamine has been introduced into the side chain of a polyphosphazene (see, for example, The 42th Polymer Meeting, Preprints 20J21 (1993)) have been proposed.
Depending on the application, these charge-transporting materials (charge-transporting polymers) are required to have various characteristics such as solubility, film-forming ability, mobility, heat resistance and matching in respect of oxidation potential. In order to satisfy these requirements, an introduction of a substituent is usually conducted, and the properties of the materials are thereby controlled.
Moreover, the physical properties of a charge-transporting polymer have a correlation with the physical properties of a charge-transporting monomer used as the raw material. Therefore, the method of designing the molecular structure of the charge-transporting monomer, namely, a low-molecular material, becomes critical.
For instance, monomers used as the raw material for the above-described triarylamine polymer can be roughly classified into two types, namely, (1) dihydroxyarylamine and (2) bishydroxyalkylarylamine. However, since dihydroxyarylamine has an aminophenol structure, it is susceptible to oxidation and is accordingly difficult to purify. In particular, when it has a parahydroxy-substituted structure, dihydroxyarylamine becomes even more unstable. Furthermore, because it has a structure in which an aromatic ring is directly substituted with oxygen, dihydroxyarylamine has posed problems of generating a biased charge distribution, attributable to electron attractivity caused by oxygen, thus leading to reduced mobility. On the other hand, bishydroxyalkylarylamine does not have such a problem with regard to electron attractivity, since owing to the presence of a methylene group, bishydroxyalkylarylamine is not affected by oxygen. Nonetheless, synthesis of bishydroxyalkylarylamine has proved difficult. In more detail, when diarylamine or diarylbenzidine is allowed to react with 3-bromoiodobenzene, the resultant product tends to be a mixture of product materials, because bromine and iodine, present in 3-bromoiodobenzene, are both highly reactive, and therefore a reduced yield is produced. Also, another problem has been that alkyl lithium and ethylene oxide, employed when bromine is made into a lithium product, are dangerous and highly toxic, and thus require the greatest care in handling.
Moreover, the aforementioned organic electroluminescent elements produced from the π conjugate polymer represented by paraphenylenevinylene (PPV), or from the polymer in which triphenylamine has been introduced into the side chain of a polyphosphazene, have deficiencies in terms of properties of tone, luminous intensity, durability and the like.
Therefore, in order to develop organic electronic devices such as organic electroluminescent elements which exhibit higher luminous intensity and good stability even when they are used repeatedly, it is desirable to develop organic electronic materials which can be readily synthesized, and which also have both high charge-transporting properties and excellent luminous properties.